A primary-side sampled feedback system includes a sample acquisition phase during which the voltage across the clamp capacitor is sensed as a measure of the primary-reflect output voltage. One end of the clamp capacitor is ground-referenced during the sample acquisition phase. The sample circuitry, which may include a transformer-coupled input for receiving the gate drive of the secondary switch, may use secondary-side or primary and secondary side signals to generate the sample acquisition control pulse and clamp switch drive signal. The sample acquisition control pulse occurs when the secondary current reaches its minimum or zero.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for converting power via a transformer from an input source for delivery to a load comprising: providing a primary power circuit including a primary winding of the transformer, at least one primary switch connected to drive the primary winding, a clamp capacitor, and a clamp switch to connect the clamp capacitor to the primary winding; providing secondary circuitry including a secondary winding of the transformer and rectification circuitry connected to the secondary winding and to deliver a rectified output voltage to the load; providing a switch controller to operate the at least one primary switch and the clamp switch in a series of converter operating cycles; each converter operating cycle being characterized by a current in the secondary winding varying between a maximum value and a minimum value; detecting when the current in the secondary winding essentially reaches the minimum value and generating a first signal in response; and sampling a voltage in the primary power circuit in response to the first signal as a measure of the output voltage.
2. A method comprising: converting power, received at an input from an input source at an input voltage, via a transformer for delivery to a load at an output voltage, in a series of converter operating cycles; wherein each converter operating cycle includes the following: (a) transferring energy from the input source to a primary winding of the transformer during an energy-storage phase characterized by an average value of primary current flowing in the primary winding, the average value of primary current has a first polarity, and the average is taken over the duration of the energy-storage phase, (b) transferring energy from a secondary winding of the transformer to the load during an energy-transfer phase characterized by connecting a clamp capacitor to the transformer, and (c) sensing a voltage across the clamp capacitor during a sample-acquisition phase characterized by the voltage across the clamp capacitor during the sample-acquisition phase being essentially a function of the primary reflected output voltage; and controlling the output voltage as a function of the sensed voltage across the clamp capacitor.
3. The method of claim 1 wherein each converter operating cycle includes a first time interval during which the current in the secondary winding remains essentially equal to the minimum value and one end of the primary winding is connected to a common reference potential.
4. The method of claim 1 wherein the sampling a voltage in the primary power circuit comprises sensing a voltage across the clamp capacitor.
5. The method of claim 1 wherein the sampling a voltage in the primary power circuit comprises sensing a voltage across the primary winding.
6. The method of claim 1 wherein the minimum value is essentially zero current.
7. The method of claim 1 wherein each converter operating cycle further comprises an energy-transfer phase during which energy is transferred from the secondary winding to the load and the current in the secondary winding decreases to essentially zero current.
8. The method of claim 1 wherein each converter operating cycle further comprises an energy transfer phase during which energy is transferred from the secondary winding to the load and which is terminated before the current in the secondary winding decreases to essentially zero current.
9. The method of claim 2 wherein the sample-acquisition phase is not coincident with other phases of the converter operating cycle.
10. The method of claim 9 wherein the sample acquisition phase occurs after the energy transfer phase.
11. The method of claim 2 wherein the sample-acquisition phase is coincident with at least one other phase of the converter operating cycle.
12. The method of claim 11 wherein the sample acquisition phase occurs during the energy storage phase.
13. The method of claim 2 wherein the sample acquisition phase occurs anytime during the converter operating cycle except during the energy-transfer phase.
14. The method of claim 2 wherein each converter operating cycle further comprises (d) a clamp phase during which the primary winding of the transformer is clamped, the clamp phase being characterized by essentially zero voltage across said primary winding and an average value of current flowing in the primary winding, the average value of current having a second polarity, wherein the average is taken over the duration of the clamp phase and the second polarity is opposite of the first polarity.
15. The method of claim 14 wherein the sample acquisition phase occurs during the clamp phase.
16. The method of claim 2 wherein the voltage across the clamp capacitor during the sample phase is essentially equal to the primary reflected output voltage.
17. The method of claim 2 wherein the sample acquisition phase is further characterized by essentially zero current flowing in the secondary winding.
18. The method of claim 2 wherein one end of the primary winding is connected to a common reference terminal during at least a portion of the converter operating cycle.
19. The method of claim 2 wherein one end of the primary winding is connected to a common reference terminal during the sample acquisition phase.
20. The method of claim 2 wherein the energy transfer phase is further characterized by one end of the primary winding being connected to a common reference terminal.
21. The method of claim 2 wherein the energy transfer phase is further characterized by the current in the secondary winding decreasing to essentially zero.
22. The method of claim 2 wherein the energy transfer phase is terminated before the current in the secondary winding decreases to essentially zero current.
23. The method of claim 1 or 2 further comprising forming a resonant circuit including the primary winding and the clamp capacitor.
24. The method of claim 2 further comprising: detecting when a current in the secondary winding essentially reaches a minimum value during the energy-transfer phase and generating a first signal in response; and initiating the sample-acquisition phase in response to the first signal.
25. The method of claim 24 wherein the detecting comprises sensing a change in polarity of a voltage across a secondary switch.
26. The method of claim 24 wherein the detecting comprises sensing a change in voltage across the secondary winding.
27. The method of claim 24 wherein the detecting comprises sensing a change in a control signal for operating a secondary switch.
28. The method of claim 24 wherein the detecting comprises sensing when a secondary switch opens.
29. The method of claim 24 wherein the detecting comprises sensing a change in voltage across a rectifier connected to the secondary winding.
30. The method of claim 24 wherein the detecting comprises sensing a current in the secondary winding.
31. The method of claim 1 wherein the rectification circuitry comprises a secondary switch and the detecting comprises sensing a change in polarity of a voltage across the secondary switch.
32. The method of claim 1 wherein the detecting comprises sensing a change in voltage across the secondary winding.
33. The method of claim 1 wherein the rectification circuitry comprises a secondary switch and the first signal is generated from a control signal for operating the secondary switch.
34. The method of claim 1 wherein the detecting comprises sensing a change in voltage across a portion of the rectification circuitry.
35. The method of claim 1 wherein the detecting comprises sensing the current in the secondary winding.
36. Apparatus for converting power via a transformer from an input source for delivery to a load comprising: a primary power circuit including a primary winding of the transformer, at least one primary switch connected to drive the primary winding, a clamp capacitor, and a clamp switch to connect the clamp capacitor to the primary winding; secondary circuitry including a secondary winding of the transformer and rectification circuitry connected to the secondary winding and to deliver a rectified output voltage to the load; a switch controller to operate the at least one primary switch and the clamp switch in a series of converter operating cycles, each converter operating cycle being characterized by a current in the secondary winding varying between a maximum value and a minimum value; the controller to detect when the current in the secondary winding essentially reaches the minimum value and generate a first signal in response, and to sample a voltage in the primary power circuit in response to the first signal as a measure of the output voltage.
37. Apparatus for converting power from an input source at an input voltage for delivery to a load at an output voltage, the apparatus comprising, a transformer having a primary winding and a secondary winding, secondary circuit elements connected to the secondary winding to deliver power to the load at the output voltage, active clamp circuitry connected to the transformer and including a clamp switch and a clamp capacitor, one or more primary switches connected to the primary winding, a switch controller to operate the clamp switch and the one or more primary switches in a series of converter operating cycles, each converter operating cycle comprising the following phases: (a) an energy-storage phase during which energy is transferred from the input source to the primary winding of the transformer and characterized by an average value of primary current flowing in the primary winding, the average value of primary current having a first polarity, and the average being taken over the duration of the energy-storage phase, (b) an energy-transfer phase during which energy is transferred from the secondary winding of the transformer to the load and characterized by connecting the clamp capacitor to the transformer, and (c) a sample-acquisition phase during which a voltage across the clamp capacitor is sensed and characterized by the voltage across the clamp capacitor during the sample-acquisition phase being essentially a function of the primary reflected output voltage; and wherein the controller is to control the output voltage as a function of the sensed voltage across the clamp capacitor.
38. The apparatus of claim 36 wherein each converter operating cycle includes a first time interval during which the current in the secondary winding remains essentially equal to the minimum value and one end of the primary winding is connected to a common reference potential.
39. The apparatus of claim 36 wherein the controller is to sample a voltage across the clamp capacitor.
40. The apparatus of claim 36 wherein each converter operating cycle further comprises an energy-transfer phase during which energy is transferred from the secondary winding to the load and the current in the secondary winding decreases to essentially zero current.
41. The apparatus of claim 36 wherein each converter operating cycle further comprises an energy transfer phase during which energy is transferred from the secondary winding to the load and which is terminated before the current in the secondary winding decreases to essentially zero current.
42. The apparatus of claim 37 wherein the sample-acquisition phase occurs during the energy storage phase.
43. The apparatus of claim 37 wherein each converter operating cycle further comprises (d) a clamp phase during which the primary winding of the transformer is clamped, the clamp phase being characterized by essentially zero voltage across said primary winding and an average value of current flowing in the primary winding, the average value of current having a second polarity, wherein the average is taken over the duration of the clamp phase and the second polarity is opposite of the first polarity.
44. The apparatus of claim 37 wherein the controller further detects when a current in the secondary winding essentially reaches a minimum value during the energy-transfer phase and generate a first signal in response; and initiate the sample-acquisition phase in response to the first signal.
45. The apparatus of claim 36 wherein the rectification circuitry comprises a secondary switch and the controller is to detect a change in polarity of a voltage across the secondary switch.
46. The apparatus of claim 36 wherein the rectification circuitry comprises a secondary switch and the first signal is generated from a control signal for operating the secondary switch.
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November 20, 2006
December 28, 2010
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